Given volume of a piece of iron = 30 cm3, Mass = 234 g.
| (i) Density | = | Mass/Volume |
| = | 234 g/30 cm3 | |
| = | 7.8 g cm–3 | |
| (ii) Density | = | Mass/Volume |
| = | [234/1000] kg/[30/(100)3] m3 | |
| = | 7800 kg m–3 |
Given a piece of copper of mass = 106 g
| (i) Volume of copper piece | = | (30 – 18) cm3 |
| = | 12 cm3 | |
| (ii) Density of copper | = | Mass/Volume |
| = | 106 g/12 cm3 | |
| = | 8.83 g cm–3 |
The mass of the density bottle is 14 g when empty, 40.5 g when full of water and 35.85 g when full of paraffin oil. Calculate the density of oil and state the assumption made?
| Mass of oil | = | (35.85 – 14) g = 21.85 g |
| Mass of water | = | (40.5 – 14) g = 26.50 g |
| Since the density of water is 1 g cm–3, | ||
| volume of water | = | 26.50 cm3 which is equal to the volume of oil. |
| Density of oil | = | Mass/Volume |
| = | 21.85 g/26.50 cm3 | |
| = | 0.82 g cm–3. | |
| Assumption: | ||
| The density of water | = | 1 g cm–3. |
The volume of a balloon is 1000 m3. It is filled with helium of density 0.2 kg m–3. What load can it lift ? Density of air is 1.29 kg m–3?
| Weight of helium filled in balloon | = | V × d × g |
| = | 1000 × 0.2 × g | |
| = | 200 g N | |
| = | 200 kgf | |
| Weight of air displaced | = | upthrust |
| = | V × density of air × g | |
| = | 1000 × 1.29 × g | |
| = | 1290 g N | |
| = | 1290 kgf | |
| Resultant upward force on balloon | = | 1290 – 200 |
| = | 1090 kgf. | |
| So, it can lift 1090 kgf load. |